1. Field of the Invention
The present invention relates to a slit illumination system for copying machines and the like, and more particularly to a slit illumination system having high illumination efficiency and uniform illumination distribution.
2. Description of the Related Art
A conventional slit illumination system for a copying machine and the like is explained with reference to FIG. 1.
In FIG. 1, an original (not shown) is placed on a document glass table 6. A document surface 6a represents an upper surface of the document glass table 6. A slit illumination system 7 for illuminating the document surface 6a from the below is composed of an elongated exposure lamp 2 as a light source, a main reflecting mirror 1 and an auxiliary reflecting mirror 4 which encompasses the exposure lamp 2 with the main reflecting mirror 1.
The main reflecting mirror 1 includes four portions 1a to 1d. Each of the portions 1a and 1c is a part of an ellipsoid having its first focus at a slit-illuminated position 3 on the document surface 6a to be slit-illuminated and its second focus at the center of the exposure lamp 2. Each of the portions 1b and 1d is a part of an ellipsoid having its first focus at the center of the exposure lamp 2 and its second focus at a point 3' symmetrically to the slit-illuminated position 3 on the document surface 6a with respect to the auxiliary reflecting mirror 4.
Accordingly, the rays of light emitted from the exposure lamp 2 are condensed at the slit-illuminated position 3 as shown by leftwardly upward and rightwardly upward hatching in FIG. 1 in order to slit-illuminate the document surface 6a. An original image to be illuminated is directed from the slit-illuminated position 3 to a lens system (not shown) through a slit 5 formed between the main and auxiliary reflecting mirrors 1 and 4 and further to a photosensitive member, so that the photosensitive member is efficiently exposed.
Recently, the high-speed copying and the color copying are remarkably improved in electrophotographic copying machines, digital copying machines, printer, facsimile and the like. These improvements require a slit illumination system having a high illumination efficiency.